Cellular fixed networks are generally formed of a plurality of base transceiver stations (BTSs) which wirelessly contact mobile units (referred to also as mobile stations and/or cellular handsets), serviced by the network. The BTSs are connected, usually in a tree topology, to a regional base station controller (BSC) which controls the routing of calls in the network. In the tree topology, one or more of the BTSs are connected directly to the BSC, and the other BTSs connect to the BSC through other BTSs which serve as relay units. The links of the tree are formed of cables which comprise a predetermined number of channels according to the capacity of the link. Each channel includes bandwidth sufficient for passing the signals of a single telephone call at the rate of 16 Kbit/sec. A commonly used link is the E1 link which includes 120 channels. Alternatively, each channel includes bandwidth sufficient for passing the signals of a single telephone call at the rate of 8 Kbit/sec, and in such a case an E1 link includes 240 channels.
When a mobile unit participates in a telephone call, the BSC allocates, using circuit switching, a connection from the BSC to the BTS servicing the mobile. The allocated connection is formed of dedicated channels which are used only for signals passed to and from the mobile unit to which the connection was allocated, and the allocation remains in effect until the telephone call is terminated. During the call, the mobile unit converts input signals into digital signals. As the use of wireless bandwidth is very costly, the digital signals are compressed by the mobile unit, and the compressed signals are transmitted to the servicing BTS. Generally, every 20 msec the mobile unit generates a packet of 320 bits which represents the sounds collected by the mobile unit during a time period of 20 msec.
The servicing BTS passes the compressed signals as they are, without decompressing them, to the BSC, over the mobile's dedicated channels. The BSC usually decompresses the signals and transfers them to a Mobile switching Center (MSC) or to a public network to which the signals are directed.
Generally, each packet comprises a header and a payload. Exemplary headers are formed of 8 synchronization bits and 24 control bits or of 16 synchronization bits and 16 control bits. It is noted that other header structures exist, including encapsulations which distribute the control bits throughout the packets.
With the increase in usage of cellular phones the number of calls carried out concurrently by a single BTS and the number of concurrently allocated channels on a single link increased substantially. As the signals sent from the BTSs to the BSC are already compressed, further compression would degrade the signals below current quality standards.
Therefore, in order to supply the demand, additional cables and/or cables of larger bandwidth must be laid between the BSC and the BTSs. In some densely populated areas the laying of cables may be very costly.